Yoke compartment of voice coil motor for hard disk drive and voice coil motor using said yoke compartment

ABSTRACT

A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, includes a first step of subjecting the yoke component to a barrel polishing treatment; and a second step of subjecting the yoke component to at least one of an abrasive grain fluidization treatment, a thermal deburring treatment, a magnetic polishing treatment, an ultrasonic deburring treatment, and a water jet deburring treatment.

This application is a Divisional of application Ser. No. 09/658,014,filed on Sep. 8, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to a yoke component for making up amagnetic circuit of a voice coil motor for a hard disk drive, and amethod of deburring the surface of the yoke component, and particularlyto a method of deburring a yoke component, which is capable of removingburrs produced on all ridge lines, including ridge lines at finelymachined portions, of the yoke component. The present invention alsorelates to a voice coil motor for a hard disk drive, using the yokecomponent from which burrs are thus removed.

A voice coil motor for a hard disk drive includes, as shown in FIG. 1, arare-earth magnet “a” and a yoke component “b” for making up a magneticcircuit of the voice coil motor. In addition, character “c” designates acoil. In recent years, along with a tendency to increase the storagecapacities of hard disks, flying heights of magnetic heads have come tobe reduced, and to prevent occurrence of head crush due to thereductions in flying heights of the magnetic heads, voice coil motorshave been increasingly required to be cleaned.

Of components of a voice coil motor, a yoke component manufactured bypressing or cutting has a disadvantage that it has high viscositycausing shearing burrs or cutting burrs. This is because the yokecomponent is mainly made from a low carbon steel having a high toughnessfor obtaining an excellent motor performance.

Further, in recent years, since hard disk drives have been miniaturized,yoke components for making up magnetic circuits of voice coil motorsused for the hard disk drives have come to be miniaturized and to becomplicated in shape. As a result, the number of yoke components havingfinely machined portions such as through-holes, bends, and threadedholes has been increased, thereby tending to increase the frequency ofoccurrence of burrs. For example, in a yoke component thus miniaturizedand complicated in shape, shearing burrs or cutting burrs of 0.5 mm orless in thickness are often produced in through-holes or threaded holesof about 3 mm in diameter. These burrs adhering on the surface of theyoke component do not necessarily remain adhering thereon but may beeasily dropped therefrom due to physical or chemical causes.

Even if burrs are not dropped from the surface of a yoke component,since the surface of the yoke component is subjected to nickel plating,the nickel plating film on the surface may be crushed and a nickelpowder be dropped therefrom when an external impact force is applied tothe burrs.

The drop of burrs leads to deterioration of the cleanness of a voicecoil motor for a hard disk drive, and further causes head crush and thelike if the dropped burrs collide with a magnetic head upon operation ofthe hard disk drive. In particular, since the flying height of amagnetic head has been recently reduced to 0.1 μm or less, the drop ofburrs of 0.5 mm or less in thickness has become a cause of head crush.

If a dropped burr adheres on a hard disk, there arises a problemassociated with breakage of data recorded in the hard disk because ofthe ferromagnetic property of the burr. In recent years, since therecording density of a hard disk has become 1 GB/cm² or more, the dropof a burr of about 0.5 mm in thickness has possibly led to seriousbreakage of data recorded in the hard disk.

To remove burrs on yoke components for making up magnetic circuits ofvoice coil motors for hard disk drives, various kinds of deburringmethods have been proposed; however, any one of these methods has notsucceeded to perfectly remove burrs on yoke components. For example, adeburring method using a barrel polishing treatment is effective toremove large burrs produced on ridge lines around the outer periphery ofa yoke component; however, such a method is disadvantageous in thatburrs of 0.5 mm or less in thickness present on finely machinedportions, such as through-holes, bends, and threaded holes, of the yokecomponent cannot be removed because abrasive grains do not sufficientlycollide therewith.

A burring method using a chemical polishing treatment is effective toremove micro-burrs of 0.1 mm or less in thickness present at anylocation of a yoke component; however, such a method is disadvantageousin that burrs of more than 0.1 mm and 0.5 mm or less in thicknesspresent on a yoke component cannot be removed by dissolution because ofa possibility that longer chemical polishing may dissolve the main bodyof the yoke component. In general, the chemical polishing treatment isadditionally used to make small burrs of 0.5 mm or less present onfinely machined portions such as through-holes, bends, or threadedholes, which burrs cannot be removed by barrel polishing because theabrasive grains are larger in size than the finely machined portions,and as described above, the chemical polishing treatment has not effectof perfectly removing such burrs of 0.5 mm or less.

A deburring method using an abrasive grain fluidization treatment iseffective to remove whisker-like burrs having fine roots, producedtypically upon cutting of a yoke component, by pressing viscoelasticmedia containing abrasive grains kneaded therein to burrs; however, sucha method is disadvantageous in that burrs produced by shearing, whichhave roots wider than tips, cannot be perfectly removed at the roots.Further, a deburring method using a thermal deburring treatment isdisadvantageous in that heat generated at burrs are easy to propagate tothe main body of a yoke component, thereby making it difficult to removethe burrs by oxidation; a deburring method using a magnetic polishingtreatment is disadvantageous in that even if needle media made from aferromagnetic material collide with a burr, the burr cannot be removedat the root; and a deburring method using ultrasonic vibration or waterpressure is disadvantageous in that burrs produced by shearing cannot beremoved at the roots, and therefore, these methods are not generallyused for deburring yoke components for making up magnetic circuits ofvoice coil motors for hard disk drives.

A prior art deburring method has generally used only the barrelpolishing treatment or the barrel polishing treatment followed by thechemical polishing treatment to deburr yoke components for making upmagnetic circuits of voice coil motors for hard disk drives; however,such a method has failed to remove burrs of 0.5 mm or less in thicknesspresent on finely machined portions, such as through-holes, bends, andthreaded holes, of a yoke component, and in some cases, the prior artmethod has adopted brushing to remove such burrs.

The brushing for finely machined portions on which fine burrs areproduced, however, is difficult to be automated because the shapes ofyoke components differ for each voice coil motor, and therefore, suchbrushing must be manually performed, to cause a problem in that thedeburring cost is raised.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a yoke component formaking up a magnetic circuit of a voice coil motor for a hard diskdrive, which yoke component has no burr on all ridge lines,particularly, ridge lines at finely machined portions, of the yokecomponent; to provide a method of deburring a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichis capable of certainly, efficiently deburring the yoke component; andto provide a voice coil motor for a hard disk drive, using a yokecomponent from which burrs are thus removed.

The present inventor has made examination to achieve the above object,that is, to certainly, efficiently deburr a yoke component made from alow carbon steel on which burrs are produced upon shearing or cuttingwork of the yoke component, and found that burrs present on all ridgelines, particularly, ridge lines at finely machined portions (forexample, through-holes, threaded holes and recesses, each of which hasan diameter of 10 mm or less, and further bends each having a radius ofcurvature of 5 mm or less) are difficult to be removed only by a barrelpolishing treatment because abrasive grains cannot be sufficientlycollide with the burrs present on the finely machined portions; however,these burrs present on all ridge lines of the yoke component can becertainly removed by subjecting the yoke component to the barrelpolishing treatment, and then subjecting the yoke component to at leastone of a thermal deburring treatment, a magnetic polishing treatment, anultrasonic deburring treatment, and a water jet deburring treatment. Thepresent inventor has thus accomplished the present invention on thebasis of the above-described knowledge.

Therefore, according to a first aspect of the present invention, thereis provided a yoke component, made from a low carbon steel, for makingup a magnetic circuit of a voice coil motor for a hard disk drive,wherein the yoke component has on any ridge line thereof no burr of 0.5mm or less in thickness.

According to a second aspect of the present invention, there is provideda deburring method of removing burrs present on the surface of a yokecomponent, made from a low steel carbon steel, of a voice coil motor fora hard disk drive, including: a first step of subjecting the yokecomponent to a barrel polishing treatment; and a second step ofsubjecting the yoke component to at least one of an abrasive grainfluidization treatment, a thermal deburring treatment, a magneticpolishing treatment, an ultrasonic deburring treatment, and a water jetdeburring treatment.

According to a third aspect of the present invention, there is provideda voice coil motor for a hard disk drive, including: a yoke component,made from a low carbon steel, for making up a magnetic circuit of thevoice coil motor, wherein the yoke component has on any ridge linethereof no burr of 0.5 mm or less in thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a voice coil motor;

FIGS. 2A and 2B are views typically showing two kinds of forms of burrspresent on a yoke component, wherein FIG. 2A shows a shearing burrproduced on a yoke component upon pressing work of the yoke component,and FIG. 2B shows a whicker-like burr produced on a yoke component uponcutting work of the yoke component; and

FIGS. 3A to 3D are views typically showing steps of removing burrspresent at the opening edge of a through-hole of a yoke component,wherein FIG. 3A shows a state before barrel polishing; FIG. 3B shows astate after barrel polishing; FIG. 3C shows a state after abrasive grainfluidization treatment; and FIG. 3D shows a state after chemicalpolishing.

DETAILED DESCRIPTION OF THE INVENTION

Burrs to be removed by a deburring method of the present invention areburrs of 0.5 mm or less in thickness produced on all ridge lines,particularly, ridge lines at finely machined portions, of a yokecomponent made from a low carbon steel for making up a magnetic circuitof a voice coil motor for a hard disk drive. FIGS. 2A and 2B are viewstypically showing two kinds of forms of burrs and defining a thicknessof each burr, wherein FIG. 2A shows a shearing burr produced on a yokecomponent upon pressing work of the yoke component, and FIG. 2B shows awhisker-like burr produced on a yoke component upon cutting work of theyoke component. The forms of burrs to be removed by the deburring methodof the present invention, however, are limited thereto.

The deburring method of the present invention includes: (1) a first stepof subjecting a yoke component, on which burrs of the above-describedforms are present, to a barrel polishing treatment; and (2) a secondstep of subjecting the yoke component to at least one of an abrasivegrain fluidization treatment, a thermal deburring treatment, a magneticpolishing treatment, an ultrasonic deburring treatment, and a water jetdeburring treatment. Additionally, the deburring method of the presentinvention may include (3) a third step of subjecting the yoke componentto a chemical polishing treatment as needed.

Hereinafter, each of the above-described treatments of the deburringmethod of the present invention will be described.

Deburring Step by Barrel Polishing Treatment

The deburring by barrel polishing treatment is intended to remove burrson ridge lines with which abrasive grains can sufficiently collide,other than burrs on ridge lines at finely machined portions such asthrough-holes, bends, and threaded holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive. Thebarrel polishing treatment is also intended to make abrasive grainscollide to shearing burrs of 0.5 mm or less in thickness at finelymachined portions such as through-holes, bends, and threaded-holes, toforcibly roll the burrs and make thin the roots thereby by collision ofthe abrasive grain which is insufficient to remove the burrs, therebyforming the burrs into shapes easy to be removed at the subsequent stepusing at least one of the abrasive grain fluidization treatment, athermal deburring treatment, a magnetic polishing treatment, anultrasonic deburring treatment, or a water jet deburring treatment.

The barrel polishing treatment can be performed by charging a yokecomponent, abrasive grains mainly made from alumina, silica, ormagnesia, and water to which a rust-preventive solution is added, into arotary barrel, vibration barrel, or centrifugal barrel, and making theabrasive grains collide the yoke component by rotation or vibration. Theshape of each abrasive grain may be a spherical or triangular shape, andthe size of each abrasive grain may be 3 mm or more, particularly, 5 mmor more and 20 mm or less, particularly, 15 mm or less, and generally beabout 10 mm. It may be undesirable to use abrasive grains each having asize smaller than that described above, that is, less than 3 mm. This isbecause such small abrasive grains may remain in threaded holes orrecesses. The barrel polishing treatment can remove burrs, each having athickness ranging from 0.5 mm to 1.0 mm, produced on ridge lines withwhich abrasive grains can sufficiently collide along various directions,other than burrs produced at finely machined portions such asthrough-holes, bends, and threaded holes, of the yoke component. Thebarrel polishing treatment, however, cannot remove but only rollshearing burrs of 0.5 mm or less in thickness produced at finelymachined portions such as through-holes, bends, and threaded holesbecause abrasive grains collide with the burrs along limited directions.Here, as the effect of the barrel polishing treatment, although theshearing burrs of 0.5 mm or less cannot be removed by the barrelpolishing treatment, the roots thereof become thinner than those of theoriginal burrs before barrel polishing, and therefore, such burrs areeasy to be removed at the subsequent step using at least one of theabrasive grain fluidization treatment, a thermal deburring treatment, amagnetic polishing treatment, an ultrasonic deburring treatment, or awater jet deburring treatment.

According to the prior art deburring method, shearing burrs of 0.5 mm orless in thickness produced at finely machined portions, such asthrough-holes, bends, and threaded holes, of a yoke component, whichcannot be removed by the barrel polishing treatment, are left as theyare or are made smaller by additional chemical polishing. It should benoted that as described above, the additional chemical polishing failsto perfectly remove the shearing burrs of 0.5 mm or less which haveremained after barrel polishing.

Deburring Step by Abrasive Grain Fluidization Treatment

The deburring by abrasive grain fluidization treatment is intended toremove burrs of 0.5 mm or less produced at finely machined portions,such as through-holes, bends, and threaded holes, of a yoke componentfor making up a magnetic circuit of a voice coil motor for a hard diskdrive, which burrs cannot be removed by barrel polishing.

The abrasive grain fluidization treatment is performed by mechanicallypressing special clay-like viscoelastic media containing abrasive grainskneaded therein to a portion to be deburred, thereby deburring theportion. In this case, the elastic effect of the viscoelastic media isadded to the abrasive grains kneaded therein, to produce a polishingpressure and a moving speed of abrasive grains necessary for polishingthe portion to be deburred. In this treatment, there is used anapparatus capable of pressing the viscoelastic media in both the upwardand downward directions, to reciprocally move the media, therebyenhancing the deburring ability.

In the case of removing burrs present at finely machined portions, suchas through-holes, bends, and treaded holes, of a yoke component formaking up a magnetic circuit of a voice coil motor for a hard disk driveby using the above-described apparatus, a flow passage to fluidize themedia to the portion to be deburred is formed in matching to the portionto be deburred by using a jig. In this case, for enhancing themass-productivity by simultaneously performing the abrasive grainfluidization treatment to a plurality of yoke components, flow passagesmay be formed by the jigs in such a manner as to be matched to theplurality of yoke components laminated to each other. Theviscoelasticity of the media is not particularly limited but may bepreferably not high so much if the media is used for removing burrs of0.5 mm or less present at finely machined portions, such asthrough-holes, bends, and treaded holes, of a yoke component for makingup a magnetic circuit. To easily remove the media from a yoke componenthaving been subjected to abrasive grain fluidization, fat and oil may bepreviously contained in the media. The material of the abrasive grainskneaded in the media may be selected from silicate carbide, boroncarbide, or diamond, and the particle size thereof is selected in arange of #50 to #500 in accordance with the production state of burrs tobe removed. The pressure may be selected in a range of 10 to 100 kg/cm²in accordance with the production state of burrs to be removed. Sincethe through-holes, threaded holes, or recesses are filled with the mediaafter the deburring by abrasive grain fluidization, the media isrequired to be removed therefrom by air cleaning or water cleaning. Withthis abrasive grain fluidization treatment, shearing burrs of 0.5 mm orless in thickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless cannot be removed by the prior art single abrasive grainfluidization treatment.

Whisker-like burrs having fine roots, which are produced at finelymachined portions, such as threaded holes or recesses, upon cutting workof a yoke component, can be perfectly removed by collision of theabrasive grains therewith during the abrasive grain fluidizationtreatment.

The apparatus used for the abrasive grain fluidization treatment hasbeen described in [“Deburring Method Using Abrasive Grain FluidizationTreatment”, Mechanical Technology, Vol. 36, No. 9 (the August Number in1988), Nikkan Kogyo Shinbunsha K. K.].

If the deburring by abrasive grain fluidization is performed withoutbarrel polishing as the previous step, as described above, shearingburrs which have roots wider than tips cannot be removed at the rootseven if the viscoelastic media containing abrasive grains kneadedtherein are pressed to the burrs, and therefore, shearing burrs on allridge lines, including burrs at finely machined portions, cannot beremoved at all.

Deburring Step by Thermal Deburring Treatment

The deburring by thermal deburring treatment is intended to remove burrsof 0.5 mm or less produced at finely machined portions, such asthrough-holes, bends, and threaded holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing.

The thermal deburring treatment is performed by putting yoke componentsin a gastight combustion chamber, gastightly closing the combustionchamber, and feeding a compressed combustion gas in the combustionchamber through a burnable gas inlet. The feed pressure of thecombustion gas may be set in a range of 3 to 10 atm in accordance withthe number of yoke components and the production state of burrs to beremoved. To avoid deformation of yoke components, the feed pressure ofthe combustion gas may be set at a value being as small as possible. Thecomposition of the combustion gas is represented by CH₄:O₂=1:2.5. Thatis to say, the combustion gas contains oxygen in an amount larger thanthat necessary for combustion of methane. The excess oxygen is consumedfor combustion of burrs. Accordingly, the optimum mixing ratio of thecombustion gas may be set at a value matched to the production state ofburrs in order to prevent part of the burrs from remaining due to thelack of combustion by insufficient oxygen or to avoid significantoxidation of the main body of the yoke component due to excess oxygen.

When the combustion gas supplied in the combustion chamber is ignited byan ignition plug, such a combustion gas is instantly burned, to causeheat waves of about 3000° C., thereby removing burrs by oxidation. Atthis time, the surface of the main body of the yoke component isslightly oxidized to form an oxide film. Such an oxide film may bedesirable to be removed by acid cleaning or the like after the thermaldeburring treatment. With this thermal deburring treatment, shearingburrs of 0.5 mm or less in thickness present at finely machinedportions, particularly, at through-holes and bends formed by punchingcan be removed in combination with the effect of the previous step usingbarrel polishing, that is, the effect of forcibly rolling the burrsthereby making thin the roots thereof. It should be noted that the aboveshearing burrs of 0.5 mm or less cannot be removed by the prior artsingle thermal deburring treatment.

Whisker-like burrs having fine roots, which are produced at finelymachined portions, such as threaded holes or recesses, upon cutting workof a yoke component, can be perfectly oxidized and removed by thethermal deburring treatment.

The thermal deburring apparatus has been described in [“InstantDeburring by Using Thermal Impact”, Mechanical Technology, Vol. 29, No.8, pp. 135-137 (1981)].

If the thermal deburring treatment is performed without barrel polishingas the previous step, as described above, shearing burrs which haveroots wider than tips cannot be removed by oxidation because heatgenerated at the burrs is easy to propagate to the main body of the yokecomponent, and therefore, shearing burrs on all ridge lines, includingburrs at finely machined portions, cannot be removed at all.

Deburring Step by Magnetic Polishing Treatment

The deburring by magnetic polishing treatment is intended to removeburrs of 0.5 mm or less produced at finely machined portions, such asthrough-holes, bends, and threaded holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing.

The magnetic polishing treatment is performed as follows: First,ferromagnetic stainless steel media in the forms of needles each havinga diameter of 0.2 to 1.0 mm and a length of about 5 mm and parts to bedeburred are put in a vessel. At this time, a cleaning solution forpreventing the parts to be deburred and the media from beingcontaminated is simultaneously poured in the vessel. The vessel is putin a magnetic field in which N and S poles are alternately changed. Asthe polarities of the magnetic field are quickly changed from eachother, the ferromagnetic media are repeatedly, strongly stirred andvibrated, and are inserted in finely machined portions such asthrough-holes, bends, and threaded holes, to thereby remove burrs bycollision therewith. As a method of changing the N and S poles in themagnetic field in the vessel from each other, there may be adopted amethod of disposing the vessel between electric magnets to which analternating current is applied, or a method of rotating a disk, on whichstrong magnets are provided with N and S poles alternately arranged, ata high speed under a base on which the vessel is mounted.

In general, parts to be deburred by magnetic polishing are non-magneticbodies. Ferromagnetic parts are difficult to be deburred by magneticpolishing because such parts are moved in the same direction as that ofthe ferromagnetic media when the N and S poles in the magnetic field arechanged from each other. However, by fixing ferromagnetic parts in avessel by means of non-magnetic jigs, the media are allowed to stronglycollide with the ferromagnetic parts, thereby removing burrs presentthereon.

A yoke component is a ferromagnetic body made from a low carbon steel.Accordingly, by fixing the yoke component by means of a jig, burrspresent on the yoke component can be removed by magnetic polishing. Inthis case, to make the media certainly collide with the yoke component,the yoke component may be desirable to be fixed with its shearingdirection directed in parallel to the direction of the magnetic field.

The charged amount of yoke components is determined in accordance withthe size of a vessel in which the yoke components are to be put, and thedesign of jigs for fixing the yoke components. The frequency forchanging the polarities of a magnetic field in the vessel is set at50-60 Hz or more for strongly stirring and vibrating the media, and thechange in polarities of the magnetic field at a high frequency can beeasily performed by adopting the method of rotating a disk, on whichstrong magnets are provided with N and S poles alternately arranged, ata high speed under a base on which the vessel is mounted.

The thickness of each of the media may be selected in a range of about0.5 to 1.0 mm in accordance with the production state of burrs of 0.5 mmor less in thickness present at finely machined portions, such asthrough-holes, bends, and thread holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing. The use of the media eachhaving a thickness of about 0.2 mm reduces the deburring effect becauseof the light weights of the media. Such fine media are generally usedfor deburring resin based parts.

The polishing time is set in a range of about 1 to 10 min in accordancewith the production state of burrs, and the frequency for changing thepolarities of a magnetic field. Since the surface of the yoke componentis wet and is thereby liable to be rusted after magnetic polishing, itmay be desirable to wash the yoke component with water for removing thecleaning solution therefrom, and to dry the yoke component by using anoven or air blower.

With this magnetic polishing treatment, shearing burrs of 0.5 mm or lessin thickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless produced by punching cannot be removed by the prior art singlemagnetic polishing treatment.

Whisker-like burrs having fine roots, which are produced at finelymachined portions, such as threaded holes or recesses, upon cutting workof a yoke component, can be perfectly removed by collision of the mediatherewith during the magnetic polishing treatment.

The magnetic polishing apparatus has been described in [“MagneticPolishing Method Capable of Removing Micro-Burrs on Product withoutDeformation and Efficiently Finishing the Product” [b (2)] JA G0937ATool Engineer (JPN) 38[2] 34-39 ('97)].

If the magnetic polishing is performed without barrel polishing as theprevious step, as described above, shearing burrs which have roots widerthan tips cannot be removed at the roots even if the media composed offerromagnetic needles collide with the burrs during the magneticpolishing treatment, and therefore, shearing burrs on all ridge lines,including burrs at finely machined portions, cannot be removed at all.

Deburring Step by Ultrasonic Deburring Treatment

The deburring by ultrasonic deburring treatment is intended to removeburrs of 0.5 mm or less produced at finely machined portions, such asthrough-holes, bends, and threaded holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing.

The ultrasonic deburring treatment is performed by putting a yokecomponent to be deburred in water, and emitting strong ultrasonic wavesinto the water, to impart strong vibration to burrs on the yokecomponent by making use of cavitation (growth and extinction ofmicro-bubbles) in the resonance region of the ultrasonic waves, therebyremoving the burrs thus fatigued by vibration. The resonance region inwhich cavitation occurs is limited to a specific area calculated by thefrequency of the ultrasonic waves, and therefore, a location to bedeburred may be desirable to be fixed in the specific area.

In the case of deburring a plurality of locations of a yoke component,the yoke component suspended from a jig into water may be swung. Thefrequency of the ultrasonic waves used for this ultrasonic deburringtreatment may be as low as about 25 kHz. The use of the ultrasonic waveshaving a frequency more than 30 kHz increases the resonance region inwater but reduces the cavitation to such an extent as to make impossiblethe deburring. Meanwhile, the use of ultrasonic waves having a frequencylower than 20 kHz, which is near audio frequencies, may cause largenoise. Accordingly, the frequency of the ultrasonic waves is preferablyin a range of 20 to 30 kHz. The output of an ultrasonic wave generatorused for this ultrasonic deburring treatment may be as high as about1200 W, and ultrasonic oscillators may be densely arranged for enhancingthe deburring ability. The lower the temperature of water used forultrasonic deburring treatment, the higher the cavitation effect. Fromthis viewpoint, the temperature of water used for ultrasonic deburringtreatment may be controlled at a low temperature of 10° C. or less forincreasing the cavitation effect. Since oil or air in water obstructsthe occurrence of cavitation, the use of pure water or deaeration beforedeburring may be carried out for enhancing the deburring effect. Theultrasonic deburring treatment time may be set in a range of 30 sec to10 min in accordance with the shapes of burrs. Since the surface of theyoke component is wet and is thereby liable to be rusted afterultrasonic deburring, the yoke component may be desirable to be dried byusing an oven or air blower. With this ultrasonic deburring treatment,shearing burrs of 0.5 mm or less in thickness present at finely machinedportions, particularly, at through-holes and bends formed by punchingcan be removed in combination with the effect of the previous step usingbarrel polishing, that is, the effect of forcibly rolling the burrsthereby making thin the roots thereof. It should be noted that the aboveshearing burrs of 0.5 mm or less cannot be removed by the prior artsingle ultrasonic deburring treatment.

Whisker-like burrs having fine roots, which are produced at finelymachined portions, such as threaded holes or recesses, upon cutting workof a yoke component, can be perfectly removed by vibration due toultrasonic waves.

The ultrasonic deburring apparatus has been described in [“PreciseSurface Finish and Burr Technology-Removal of Burrs and Surface Finishby Ultrasonic Cleaning” [b(2)] JA F145A, Mechanical Technology, (JPN)44[(2)]].

If the ultrasonic deburring is performed without barrel polishing as theprevious step, as described above, shearing burrs which have roots widerthan tips cannot be removed at the roots even by vibration due toultrasonic waves, and therefore, shearing burrs on all ridge lines,including burrs at finely machined portions, cannot be removed at all.

Deburring Step by Water Jet Deburring Treatment

The deburring by water jet deburring treatment is intended to removeburrs of 0.5 mm or less produced at finely machined portions, such asthrough-holes, bends, and threaded holes, of a yoke component for makingup a magnetic circuit of a voice coil motor for a hard disk drive, whichburrs cannot be removed by barrel polishing.

The water jet deburring treatment is performed by discharging a waterjet at a high pressure 100 to 700 kg/cm² from a nozzle to a yokecomponent by a high pressure pump such as a plunger pump, therebyremoving burrs on the yoke component by collision of the water jet withthe burrs. The nozzle may be of a direct-jet type for preventing a waterjet at a high pressure from being spread, and also may have only onedischarge port for increasing the deburring ability at maximum.

The discharge pressure, distance between the nozzle and a yokecomponent, flow rate of discharged water, and discharge time should beset at such values as not to deform or damage the yoke component.Concretely, to obtain a sufficient deburring effect, the distancebetween the nozzle and the yoke component may be set in a range of 40 to100 mm; the flow rate of the discharge water may be set in a range of 10to 50 L/min, and the discharge time may be set in a range of 1 to 10sec.

First, a position or positions of one burr or a plurality of burrs of0.5 mm or less in thickness at one or a plurality of finely machinedportions, such as through-holes, bends, or threaded holes, of a yokecomponent, which burr or burrs cannot be removed by barrel polishing,has or have been previously checked. If one position of the burr hasbeen checked, the yoke component is fixed by means of a jig with such aposition directed to the nozzle, and a water jet at a high pressure isdischarged from the nozzle to the position, to thereby remove the burr.If a plurality of positions of the burrs have been checked, a water jetat a high pressure can be made to collide with the plurality of burrs onthe yoke component by moving one or both of the nozzle and the yokecomponent. Further, a water jet at a high pressure can be made tocollide with any position of a yoke component by swinging one or both ofthe nozzle or the yoke component. In the case of moving one or both ofthe nozzle and a yoke component, the moving speed may be set at a valuebeing as low as 20 mm/sec or less. If the moving speed is more than 20mm/sec, it may be difficult to ensure a sufficient deburring effect.

To increase the probability of collision of a water jet at a highpressure with burrs, the water jet may be discharged on both surfaces ofa yoke component. Since the surface of the yoke component is wet and isthereby liable to be rusted after water jet deburring, the yokecomponent may be desirable to be dried by using an oven or air blower.With this water jet deburring treatment, shearing burrs of 0.5 mm orless in thickness present at finely machined portions, particularly, atthrough-holes and bends formed by punching can be removed in combinationwith the effect of the previous step using barrel polishing, that is,the effect of forcibly rolling the burrs thereby making thin the rootsthereof. It should be noted that the above shearing burrs of 0.5 mm orless cannot be removed by the prior art single water jet deburringtreatment.

Whisker-like burrs having fine roots, which are produced at finelymachined portions, such as threaded holes or recesses, upon cutting workof a yoke component, can be perfectly removed by the impact applied by awater jet.

The water jet deburring apparatus has been described in (“AdvancedCleaning Technology Handbook”—Chapter II Physical Cleaning Media andCleaning Method, Paragraph 2 Cleaning Method, Section 5 High PressureWater Cleaning—, edited by Advanced Cleaning Technology HandbookEditorial Committee and published by K.K. Industrial Technology ServiceCenter, 1996).

If the water jet deburring treatment is performed without barrelpolishing as the previous step, as described above, shearing burrs whichhave roots wider than tips cannot be removed at the roots even if a highwater pressure is applied to the burrs, and therefore, shearing burrs onall ridge lines, including burrs at finely machined portions, cannot beremoved at all.

In rare cases, during the barrel polishing treatment as the first stepand the abrasive grain fluidization treatment or the like at secondstep, fine shearing burrs of 0.1 mm or less in thickness present atfinely machined portions of a yoke component may fall onto the main bodyof the yoke component to be in close-contact therewith. These burrscannot be perfectly removed by the first and second deburring steps. Inthese cases, it is effective to dissolve and remove the remaining burrsby a chemical polishing treatment as the finish step. The chemicalpolishing is performed by dipping a yoke component in a water solutionmainly containing 1 to 40% of hydrogen peroxide, ammonium hydrogendifluoride, or phosphoric acid for 10 sec to 10 min, thereby chemicallydissolving burrs on the yoke component.

Since the surface of the yoke component is activated after chemicalpolishing, the yoke component may be desirable to be immediatelysubjected to water washing and acid cleaning, and to nickel or copperplating. It should be noted that the abrasive grain fluidizationtreatment or the like at the second step, the chemical polishingtreatment at the final step, and plating can be continuously performedby commonly using a jig for fixing or suspending a yoke component.

FIGS. 3A to 3D typically show stages in which shearing burrs produced atthe opening edge of a through-hole are removed in the barrel polishingtreatment at the first step, the abrasive grain fluidization treatmentor the like at the second step, and the additional chemical polishingtreatment at the final step, wherein FIG. 3A shows a state before barrelpolishing; FIG. 3b shows a state after barrel polishing; FIG. 3C shows astate after abrasive grain fluidization or the like as the second step;and FIG. 3D shows a state after chemical polishing. In the figures,reference numeral 1 designates a main body of a yoke component, and 2 isa through-hole formed in the main body. In the state before barrelpolishing, shown in FIG. 3A, a fine shearing burr 11 and a shearing burr12 of 0.5 mm or less in thickness are formed at the outer peripheraledge of the through-hole 2 in such a manner as to project outwardly inthe depth direction of the through-hole 2. Since the root of each of theburrs 11 and 12 is wider than a tip thereof, such a burr cannot beremoved only by the abrasive grain fluidization treatment or the like asthe second step. When the yoke component 1 having the burrs 11 and 12 issubjected to barrel polishing (see FIG. 3B), an abrasive grain 3collides with the burrs 11 and 12, to press the burrs 11 and 12inwardly, that is, toward the inside of the through-hole 2. The barrelpolishing does not remove but roll the burrs 11 and 12, to thereby makethin the roots thereof. As shown in FIG. 3B, the fine shearing burr 11may often fall on the inner peripheral wall of the through-hole 2, andin some cases, the tip side of the burr 11 may come in contact with theinner peripheral wall of the through-hole 2. The yoke component is thensubjected to the abrasive grain fluidization treatment or the like asthe second step. At this time, as shown in FIG. 3C, since the roots ofthe burrs 11 and 12 have been made thin by barrel polishing, the burrs11 and 12 are removed by the abrasive grain fluidization treatment orthe like as the second step. In this case, there is a possibility thatthe fine shearing burr 11 having fallen on the inner peripheral wall ofthe through-hole 2 is not perfectly removed by the abrasive grainfluidization treatment or the like as the second step. As shown in FIG.3D, such a remaining portion of the fine shearing burr 11 is perfectlyremoved by chemical polishing. It should be noted that the deburringstages appeared when the deburring method of the present invention iscarried out are not limited to those shown in FIGS. 3A to 3D.

With the above-described steps, it is possible to remove all large andsmall burrs, including shearing burrs of 0.5 mm or less in thicknesspresent at finely machined portions, such as through-holes, bends, andthreaded holes, of a yoke component for making up a magnetic circuit ofa voice coil motor for a hard disk drive, which shearing burrs of 0.5 mmor less in thickness cannot be removed by the prior art single deburringstep of subjecting the yoke component to any one of the barrel polishingtreatment, abrasive grain fluidization treatment, thermal deburringtreatment, magnetic polishing treatment, ultrasonic deburring treatment,and water jet deburring treatment. The yoke component, from which allthe burrs have been removed, is then subjecting to plating, to be thusfinished as a yoke component of a voice coil motor in which thepossibility of drop of burrs harmful for a hard disk drive iseliminated.

The yoke component of the present invention is therefore characterizedin that burrs on all ridge lines, including burrs of 0.5 mm or less inthickness present at finely machined portions, such as through-holes,threaded holes and recesses each of which has an diameter of 10 mm orless, and bends each of which has a radius of curvature of 5 mm or less,of the yoke component are removed by the above-described deburringmethod of the present invention.

The voice coil motor of the present invention is therefore characterizedby adhesively bonding a magnet to the yoke component of the presentinvention, followed by magnetization, and assembling the yoke componentwith other components. It should be noted that the configurations ofother components of the voice coil motor in which the above yokecomponent is assembled may be the same as those publicly-known.

EXAMPLES

The present invention will be more clearly understood by way of, whilenot limited thereto, the following examples:

Inventive Example 1

Yoke components, each having a weight of 30 g, for making up magneticcircuits of voice coil motors for hard disk drives were prepared bypunching a cold-rolled steel sheet (grade: SPCC specified in JIS) of 3.2mm in thickness. Each yoke component having a flat-shape of about 5 cmin diagonal length has two through-holes each having an diameter of 3 mmand one rolled tap having an diameter of 2.5 mm. These through-holes androlled tap, which are opened in the thickness direction of the yokecomponent, are used for positioning the voice coil motor to the harddisk drive upon assembly thereof. The yoke component has shearing burrsproduced, upon punching of the yoke component, on all ridge lines on thepress-die side, including ridge lines of the through-holes (diameter: 3mm), and also whisker-like burrs produced, upon thread-cutting of therolled-tap (diameter: 2.5 mm), on a thread of the rolled tap. These yokecomponents are taken as test pieces. The test pieces were then subjectedin sequence to a rotary barrel polishing treatment and an abrasive grainfluidization treatment under the following conditions:

Deburring Step by Rotary Barrel Polishing Treatment

charged amount of yoke components: 50 pieces×30 g

charged amount of spherical abrasive grains mainly made from alumina orsilica (outside diameter: 15 mm): 5 kg

number of revolution: 46 rpm

polishing time: 1 hr

Deburring Step by Abrasive Grain Fluidization Treatment

media: polymer base in which powder (particle size: #320 specified inJIS) of silicon carbide is kneaded

pressure: 50 kg/cm²

pressing time for each side in reciprocating motion: 30 sec

number of reciprocating motion: one time

After barrel polishing, the two through-holes (diameter: 3 mm) and onerolled-tap (diameter: 2.5 mm) for each test piece were deburred for 1min in total by abrasive grain fluidization under the above conditions.

The test pieces thus deburred were subjected to nickel plating. Theshearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-holes (diameter: 3 mm),and whisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 1.

For comparison, the following comparative test pieces were prepared, anddeburring states of the test pieces were evaluated in the same manner asdescribed above.

Comparative Example 1

The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

The test pieces were subjected to the above-described barrel polishingtreatment and a chemical polishing treatment.

Comparative Example 3

The test pieces were subjected only to the above-described abrasivegrain fluidization treatment.

The chemical polishing treatment was performed by diluting a chemicalpolishing solution mainly containing hydrogen peroxide or ammoniumhydrogen difluoride (CPL-100, produced by Mitsubishi Gas ChemicalCompany, Inc.) by three times, and dipping each test piece in thechemical polishing solution kept at 20° C. for 1 min.

The results are shown in Table 1.

TABLE 1 ridge line at edge ridge line in ridge line on of through-holerolled-tap state of outer periphery (diameter: 3 mm) (diameter: 2.5 mm)burr shearing burr shearing burr whisker-like burr Inventive ˜0.1 mm ⊚˜0.1 mm ∘ ˜0.1 mm ⊚ Example 1 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1mm ⊚ ˜0.1 mm x ˜0.1 mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mmComparative ˜0.1 mm x ˜0.1 mm x ˜0.1 mm ⊚ Example 3 0.1 to x 0.1 to x0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm1.0 mm ⊚: burrs are perfectly removed for all yoke components observed∘: burrs are nearly perfectly removed (burrs slightly remain for someyoke components) Δ: treatment is little effective for deburring (burrsremain for most of yoke components) x: burrs are not removed at all forall yoke components observed —: burrs are not present on yoke componentsbefore deburring treatment

In Inventive Example 1, the test pieces were subjected to chemicalpolishing after abrasive grain fluidization treatment. As a result, theshearing burrs of 0.1 mm or less shown in Table 1 were perfectlyremoved.

Inventive Example 2

The same test pieces as those used in Inventive Example 1 were subjectedin sequence to a rotary barrel polishing treatment and a thermaldeburring treatment in the following conditions:

Deburring Step by Rotary Barrel Polishing Treatment

charged amount of yoke components: 50 pieces×30 g

charged amount of spherical abrasive grains mainly made from alumina orsilica (outside diameter: 15 mm): 5 kg

number of revolution: 46 rpm

polishing time: 1 hr

Thermal Deburring Treatment

composition of combustion gas: CH₄:O₂=1:2.5

charging pressure of mixed gas: 7.0 kg/cm²

charged amount of yoke components: 150 pieces

The test pieces thus deburred were subjected to nickel plating. Theshearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 2.

For comparison, the following comparative test pieces were prepared, anddeburring states of the test pieces were evaluated in the same manner asdescribed above.

Comparative Example 1

The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

The test pieces were subjected to the above-described barrel polishingtreatment and the chemical polishing treatment.

Comparative Example 4

The test pieces were subjected only to the above-described thermaldeburring treatment.

The chemical polishing treatment was performed in accordance with thesame manner as that described in Inventive Example 1.

The results are shown in Table 2.

TABLE 2 ridge line at edge ridge line in ridge line on of through-holerolled-tap state of outer periphery (diameter: 3 mm) (diameter: 2.5 mm)burr shearing burr shearing burr whisker-like burr Inventive ˜0.1 mm ⊚˜0.1 mm ∘ ˜0.1 mm ⊚ Example 2 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1mm ⊚ ˜0.1 mm x ˜0.1 mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mmComparative ˜0.1 mm x ˜0.1 mm x ˜0.1 mm ⊚ Example 4 0.1 to x 0.1 to x0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm1.0 mm The meanings of the marks ⊚, ∘, Δ, x, — in Table 2 are the sameas those of the marks ⊚, ∘, Δ, x, — in Table 1.

In Inventive Example 2, the test pieces were subjected to chemicalpolishing after thermal deburring treatment. As a result, the shearingburrs of 0.1 mm or less shown in Table 2 were perfectly removed.

Inventive Example 3

The same test pieces as those used in Inventive Example 1 were subjectedin sequence to a rotary barrel polishing treatment and a magneticpolishing treatment in the following conditions:

Deburring Step by Rotary Barrel Polishing Treatment

charged amount of yoke components: 50 pieces×30 g

charged amount of spherical abrasive grains mainly made

from alumina or silica (outside diameter: 15 mm): 5 kg

number of revolution: 46 rpm

polishing time: 1 hr

Magnetic Polishing Treatment

material of media: SUS304 (specified in JIS)

shape of media: φ0.5×5L (mm)

charged amount of media: 1 kg

dimension of vessel: φ300×150H (mm)

Under the above conditions, each yoke component was fixed to a Teflonmade jig in an upright state in the vessel and the media and water wereput in the vessel, and then the media was stirred and vibrated byalternately changing N and S poles of a magnetic field at 60 Hz for 10min.

The test pieces thus deburred were subjected to nickel plating. Theshearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 3.

For comparison, the following comparative test pieces were prepared, anddeburring states of the test pieces were evaluated in the same manner asdescribed above.

Comparative Example 1

The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

The test pieces were subjected to the above-described barrel polishingtreatment and the chemical polishing treatment.

Comparative Example 5

The test pieces were subjected only to the above-described magneticpolishing treatment.

The chemical polishing treatment was performed in accordance with thesame manner as that described in Inventive Example 1.

The results are shown in Table 3.

TABLE 3 ridge line at edge ridge line in ridge line on of through-holerolled-tap state of outer periphery (diameter: 3 mm) (diameter: 2.5 mm)burr shearing burr shearing burr whisker-like burr Inventive ˜0.1 mm ⊚˜0.1 mm ∘ ˜0.1 mm ⊚ Example 3 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1mm ⊚ ˜0.1 mm x ˜0.1 mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mmComparative ˜0.1 mm x ˜0.1 mm x ˜0.1 mm ⊚ Example 5 0.1 to x 0.1 to x0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm1.0 mm The meanings of the marks ⊚, ∘, Δ, x, — in Table 3 are the sameas those of the marks ⊚, ∘, Δ, x, — in Table 1.

In Inventive Example 3, the test pieces were subjected to chemicalpolishing after magnetic polishing treatment. As a result, the shearingburrs of 0.1 mm or less shown in Table 3 were perfectly removed.

Inventive Example 4

The same test pieces as those used in Inventive Example 1 were subjectedin sequence to a rotary barrel polishing treatment and an ultrasonicdeburring treatment in the following conditions:

Deburring Step by Rotary Barrel Polishing Treatment

charged amount of yoke components: 50 pieces×30 g

charged amount of spherical abrasive grains mainly made from alumina orsilica (outside diameter: 15 mm): 5 kg

number of revolution: 46 rpm

polishing time: 1 hr

Ultrasonic Deburring Treatment

frequency of ultrasonic waves: 25 kHz

output of ultrasonic waves: 1,200 W

water temperature: 10° C.

water quality: pure water

Under the above conditions, each yoke component was suspended by using awire, and was subjected to ultrasonic deburring for 1 min while beingswung in the vertical direction.

The test pieces thus deburred were subjected to nickel plating. Theshearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 4.

For comparison, the following comparative test pieces were prepared, anddeburring states of the test pieces were evaluated in the same manner asdescribed above.

Comparative Example 1

The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

The test pieces were subjected to the above-described barrel polishingtreatment and the chemical polishing treatment.

Comparative Example 6

The test pieces were subjected only to the above-described ultrasonicdeburring treatment.

The chemical polishing treatment was performed in accordance with thesame manner as that described in Inventive Example 1.

The results are shown in Table 4.

TABLE 4 ridge line at edge ridge line in ridge line on of through-holerolled-tap state of outer periphery (diameter: 3 mm) (diameter: 2.5 mm)burr shearing burr shearing burr whisker-like burr Inventive ˜0.1 mm ⊚˜0.1 mm ∘ ˜0.1 mm ⊚ Example 4 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1mm ⊚ ˜0.1 mm x ˜0.1 mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mmComparative ˜0.1 mm x ˜0.1 mm x ˜0.1 mm ⊚ Example 6 0.1 to x 0.1 to x0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm1.0 mm The meanings of the marks ⊚, ∘, Δ, x, — in Table 4 are the sameas those of the marks ⊚, ∘, Δ, x, — in Table 1.

In Inventive Example 4, the test pieces were subjected to chemicalpolishing after ultrasonic deburring treatment. As a result, theshearing burrs of 0.1 mm or less shown in Table 4 were perfectlyremoved.

Inventive Example 5

The same test pieces as those used in Inventive Example 1 were subjectedin sequence to a rotary barrel polishing treatment and a water jetdeburring treatment in the following conditions:

Deburring Step by Rotary Barrel Polishing Treatment

charged amount of yoke components: 50 pieces×30 g

charged amount of spherical abrasive grains mainly made from alumina orsilica (outside diameter: 15 mm): 5 kg

number of revolution: 46 rpm

polishing time: 1 hr

Water Jet Deburring Treatment

bore diameter of nozzle: 0.3 mm (direct-jet type)

discharge pressure: 500 kg/cm²

distance between nozzle and yoke component: 50 mm discharged amount ofhigh pressure water: 20 L/min

discharge time of high pressure water: 2 sec

Under the above conditions, the nozzle was positioned to each of the twothrough-holes (diameter: 3 mm) and one rolled tap (diameter: 2.5 mm),and each of the through-holes and rolled tap was deburred by a water jetfor 2 sec.

The test pieces thus deburred were subjected to nickel plating. Theshearing burrs on usual ridge line portions, shearing burrs on ridgeline portions at opening edges of the through-hole (diameter: 3 mm), andwhisker-like burrs in the rolled-tap (diameter: 2.5 mm) of each testpiece were observed. The results are shown in Table 5.

For comparison, the following comparative test pieces were prepared, anddeburring states of the test pieces were evaluated in the same manner asdescribed above.

Comparative Example 1

The test pieces were subjected only to the above-described barrelpolishing treatment.

Comparative Example 2

The test pieces were subjected to the above-described barrel polishingtreatment and the chemical polishing treatment.

Comparative Example 7

The test pieces were subjected only to the above-described water jetdeburring treatment.

The chemical polishing treatment was performed in accordance with thesame manner as that described in Inventive Example 1.

The results are shown in Table 5.

TABLE 5 ridge line at edge ridge line in ridge line on of through-holerolled-tap state of outer periphery (diameter: 3 mm) (diameter: 2.5 mm)burr shearing burr shearing burr whisker-like burr Inventive ˜0.1 mm ⊚˜0.1 mm ∘ ˜0.1 mm ⊚ Example 5 0.1 to ⊚ 0.1 to ⊚ 0.1 to ⊚ 0.5 mm 0.5 mm0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative ˜0.1mm ⊚ ˜0.1 mm x ˜0.1 mm x Example 1 0.1 to ⊚ 0.1 to x 0.1 to x 0.5 mm 0.5mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mm Comparative˜0.1 mm ⊚ ˜0.1 mm ∘ ˜0.1 mm ∘ Example 2 0.1 to ⊚ 0.1 to x 0.1 to x 0.5mm 0.5 mm 0.5 mm 0.5 to ⊚ 0.5 to — 0.5 to — 1.0 mm 1.0 mm 1.0 mmComparative ˜0.1 mm x ˜0.1 mm x ˜0.1 mm ⊚ Example 7 0.1 to x 0.1 to x0.1 to ⊚ 0.5 mm 0.5 mm 0.5 mm 0.5 to x 0.5 to — 0.5 to — 1.0 mm 1.0 mm1.0 mm The meanings of the marks ⊚, ∘, Δ, x, — in Table 5 are the sameas those of the marks ⊚, ∘, Δ, x, — in Table 1.

In Inventive Example 5, the test pieces were subjected to chemicalpolishing after water jet deburring treatment. As a result, the shearingburrs of 0.1 mm or less shown in Table 5 were perfectly removed.

As described above, the deburring method of the present invention iseffective to remove burrs on all ridge lines, including burrs on ridgelines at finely machined portions, of a yoke component for making up amagnetic circuit of a voice coil motor for a hard disk drive, andtherefore, such a method is also effective to manufacture a clean voicecoil motor from which burrs harmful to a hard disk drive are removed.

While the preferred embodiments of the present invention have beendescribed using the specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, comprising: a first step of subjecting said yoke component to a barrel polishing treatment by charging said yoke component, abrasive grains having a size of 3 mm to 20 mm, and water into a rotary barrel, vibration barrel, or centrifugal barrel and causing said abrasive grains to collide with said yoke component by rotation or vibration, thereby removing burrs each having a thickness ranging from 0.5 mm to 1.0 mm; and a second step of subjecting said yoke component to an abrasive grain fluidization treatment by mechanically pressing, at a pressure in a range of 10 to 100 kg/cm², clay-like viscoelastic media containing abrasive grains kneaded therein to a portion of said yoke component to be deburred, thereby removing burrs of 0.5 mm or less.
 2. A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, comprising: a first step of subjecting said yoke component to a barrel polishing treatment by charging said yoke component, abrasive grains having a size of 3 mm to 20 mm, and water into a rotary barrel, vibration barrel, or centrifugal barrel and causing said abrasive grains to collide with said yoke component by rotation or vibration, thereby removing burrs each having a thickness ranging from 0.5 mm to 1.0 mm; and a second step of subjecting said yoke component to a thermal deburring treatment by putting said yoke component in a gas-tight combustion chamber, gas-tightly closing the combustion chamber, feeding a compressed combustion gas into the combustion chamber through a combustion gas inlet, and igniting the combustion gas to instantly burn the combustion gas, thereby removing burrs of 0.5 mm or less by oxidation.
 3. A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, comprising: a first step of subjecting said yoke component to a barrel polishing treatment by charging said yoke component, abrasive grains having a size of 3 mm to 20 mm, and water into a rotary barrel, vibration barrel, or centrifugal barrel and causing said abrasive grains to collide with said yoke component by rotation or vibration, thereby removing burrs each having a thickness ranging from 0.5 mm to 1.0 mm; and a second step of subjecting said yoke component to an ultrasonic deburring treatment by putting said yoke component to be deburred in water, and emitting ultrasonic waves into the water so that the frequency of the ultrasonic waves is in a range of 20 to 30 kHz to impart vibration to burrs on said yoke component by making use of cavitation in the resonance region of the ultrasonic waves, thereby removing burrs of 0.5 mm or less by vibration.
 4. A deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, comprising: a first step of subjecting said yoke component to a barrel polishing treatment by charging said yoke component, abrasive grains having a size of 3 mm to 20 mm, and water into a rotary barrel, vibration barrel, or centrifugal barrel and causing said abrasive grains to collide with said yoke component by rotation or vibration, thereby removing burrs each having a thickness ranging from 0.5 mm to 1.0 mm; and a second step of subjecting said yoke component to a water jet deburring treatment by discharging a water jet at a high pressure of 100 to 700 kg/cm² from a nozzle to said yoke component by a high pressure pump, wherein the distance between the nozzle and said yoke component is set in a range of 40 to 100 mm, the flow rate of the discharge water is set in a range of 10 to 50 L/min, and the discharge time is set in a range of 1 to 10 seconds, thereby removing burrs of 0.5 mm or less by collision of the water jet with the burrs.
 5. The deburring method according to any one of claim 1, 2, 3, or 4, further comprising a third step of subjecting said yoke component to a chemical polishing treatment.
 6. The deburring method according to any one of claim 1, 2, 3, or 4, wherein said burrs have been produced by shearing work upon manufacture of said yoke component.
 7. The deburring method according to any one of claim 1, 2, 3, or 4 wherein said barrel polishing treatment is conducted in a rotary barrel, causing said abrasive grains to collide with said yoke component and thereby remove said burrs by rotation. 